08LPbypass _Std
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Transcript of 08LPbypass _Std
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• Introduction of LP Bypass system
• Overview of LP Bypass
• System details and lay out
• Control scheme of LP bypass system•
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• LP bypass bypasses steam to IPT & LPT & maintain flow
through RH.
Function of LP bypass:-1. To monitor the pressure in reheat system and to control it
under certain operating condition.
2. The volume of steam not utilized by the IPT & LPT during
start up & shut down must pass through condenser.
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LP Bypass system provide a very effective means of controlling reheat –steam flow during
LP BYPASS SYSTEM
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It enhances fast starting capability of turbines from allinitial conditions e.g.
Cold condition
Warm condition
Hot Condition
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LP steam-bypass system operates in parallel with theturbine
Protects Condenser from excessive temperature andpressure that could result from sudden injection of
superheated steam
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•
•
LP BYPASS SYSTEM
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Upon receiving load rejection signal from electricalsystem:
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• If LP steam- bypass system fails or the
condenser cannot accept LP bypass
steam , Safety Valves open and dump
steam to atmosphere
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•
•
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• Set point formation
• Pressure control for LP bypass system
• LP bypass HYDRAULIC System• Protection system
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•
•
•
Control scheme
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Set Value formation
The Two set values – fixed and variable are formed for theLPBypass control system
set value to be used is determined by a maximum valueselector
For the formation of variable set point, a pressuretransducer is used to measure the steam pressure in HPturbine
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LP Bypass System
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Features of LPBP Controller
• LPBP controller maintains pressure after reheater
by controlling LP bypass valves
• It acts on the coil of the LPBP E-H converter to
position the control valves.
• Two setpoints, fixed and variable are used in
maximum selection circuit
• Variable setpoint is derived from HP first stage
pressure
• Water spray is in two stages depending on steam
flow through LPBP stations.
• LPBP valves cannot open until adequate spray
water pressure and required vacuum is there and
condenser wall temp is not high.
• Valves can also be operated manually
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LP BYPASS SETPOINTS
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Hydraulic Mode of Operation
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•
•
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Hydraulic Mode of Operation
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•
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Design of LPBypass Valves for 210 MW
Steam Turbine
• Controlled by 8bar mineral oil
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Protection Devices
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Protection Devices cause closure of
bypass station in case of following
eventualities
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•
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CURVE FOR LPBYPASS
CONTROLLER
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Actuator Bypass
Stop Valve
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ActuatorLPBPCV
500 MW
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Pilot valve
for Water
Injection Valve
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Water
InjectionValve
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Combined Bypass
Stop & Control
Valve 210 MW
Feedback for Pilot valve of
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Feedback for Pilot valve of Bypass Control Valve 210 MW
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